/**
* Returns an InetAddress object representing the IP address of the given hostname. This name can
* be either a hostname such as "www.urbanophile.com" or an IP address in dotted decimal format
* such as "127.0.0.1". If the hostname is null or "", the hostname of the local machine is
* supplied by default. This method is equivalent to returning the first element in the
* InetAddress array returned from GetAllByName.
*
* @param hostname The name of the desired host, or null for the local loopback address.
* @return The address of the host as an InetAddress object.
* @exception UnknownHostException If no IP address for the host could be found
* @exception SecurityException If a security manager exists and its checkConnect method doesn't
* allow the operation
*/
public static InetAddress getByName(String hostname) throws UnknownHostException {
// If null or the empty string is supplied, the loopback address
// is returned. Note that this is permitted without a security check.
if (hostname == null || hostname.length() == 0) return loopback;
SecurityManager s = System.getSecurityManager();
if (s != null) s.checkConnect(hostname, -1);
// Assume that the host string is an IP address
byte[] address = aton(hostname);
if (address != null) {
if (address.length == 4) return new Inet4Address(address, null);
else if (address.length == 16) {
if ((address[10] == 0xFF) && (address[11] == 0xFF)) {
byte[] ip4addr = new byte[4];
ip4addr[0] = address[12];
ip4addr[1] = address[13];
ip4addr[2] = address[14];
ip4addr[3] = address[15];
return new Inet4Address(ip4addr, null);
}
return new Inet6Address(address, null);
} else throw new UnknownHostException("Address has invalid length");
}
// Try to resolve the host by DNS
InetAddress result = new InetAddress(null, null);
lookup(hostname, result, false);
return result;
}
private static synchronized void getLocalHost(SecurityManager s) throws UnknownHostException {
// Check the localhost cache again, now that we've synchronized.
if (s == null && localhost != null) return;
String hostname = getLocalHostname();
if (s != null) {
// "The Java Class Libraries" suggests that if the security
// manager disallows getting the local host name, then
// we use the loopback host.
// However, the JDK 1.2 API claims to throw SecurityException,
// which seems to suggest SecurityException is *not* caught.
// In this case, experimentation shows that former is correct.
try {
// This is wrong, if the name returned from getLocalHostname()
// is not a fully qualified name. FIXME.
s.checkConnect(hostname, -1);
} catch (SecurityException ex) {
hostname = null;
}
}
if (hostname != null && hostname.length() != 0) {
try {
localhost = new InetAddress(null, null);
lookup(hostname, localhost, false);
} catch (Exception ex) {
}
} else throw new UnknownHostException();
if (localhost == null) localhost = new InetAddress(loopbackAddress, "localhost");
}
/**
* Returns the hostname for this address. This will return the IP address as a String if there is
* no hostname available for this address
*
* @return The hostname for this address
*/
public String getHostName() {
if (hostName != null) return hostName;
// Lookup hostname and set field.
lookup(null, this, false);
return hostName;
}